Concertina type doors of large size are commonly used in industrial premises. In outline, such doors comprise a horizontally stiff flexible curtain constituted either by a series of hinged horizontal panels or else by a flexible sheet which is stiffened at regular intervals by horizontal stiffener rods. In both cases, door-lifting belts are fixed to the bottom of the curtain and preferably pass through guides fixed along the curtain e.g. on the hinges of some of the panels or on some of the stiffener rods. A main or belt-winding shaft runs over the top of the door for winding up the belts under electric motor drive, said shaft including brake means for locking it in position when the motor is not in operation. The motor and the brake means are commonly constituted by a combined motor and brake unit.
In present installations, if the motor is out of service (e.g. because of a breakdown or because of a power cut) and the door is closed, the door can be raised (once the brake has been released) only by means of a manually controlled emergency device comprising a handle, a shaft rotatable by the handle, and an angle coupling to enable the emergency handle to be used to rotate the main shaft and thus wind up the belts. Since large doors are heavy, such an emergency device needs to have a considerable gear reduction ratio, and as a result raising the door takes a long time. Thus, in situations which require the door to be opened quickly, e.g. to evacuate the building or to allow emergency services into the building, this type of emergency control device is inadequate. Furthermore, in current installations, when the door is open or while the door is opening, if an accident takes place which disconnects the main belt-lifting shaft from the motor and brake unit, then the curtain drops immediately under its own weight, and thus represents a potential hazard.
Preferred implementations of the present invention provide a safety and emergency actuator device for a concertina type door and suitable for preventing the door from suddenly dropping shut and also suitable for rapidly opening the door, at least partially.